The plague epidemic leads to a severe reduction in trade and industry throughout Italy, reinforcing the already existing interest of Italian princes in Jewish immigration.

Philip IV of Spain is to become famous for his patronage of his court painter Diego Velázquez.

Velázquez originates from Seville and mutual contacts had caused him to become known in 1623 to Gaspar de Guzmán, Count Duke of Olivares, Philip’s principal minister, who comes from the same region; he is summoned to Madrid by the king in 1624.

Despite some jealously from the existing court painters, Velázquez rapidly becomes a success with Philip, being retained for the rest of his career until his death, painting a celebration of the Treaty of the Pyrenees for Philip.

The king and Velázquez share common interests in horses, dogs and art, and in private are to form an easy, relaxed relationship over the years.

Velázquez is to paint at least three portraits of Olivares, his friend and original patron, producing the baroque equestrian portrait along with the standing portraits now at the Hermitage and São Paulo.

Like many contemporaries, Olivares is 'haunted' by Spain's potential decline, and sees part of the solution at least in a reform of the Spanish state.

Olivares sees Catalonia and the other provinces as paying less to the crown than they should, and does not really understand why the inhabitants should object to a fairer distribution of taxes.

He is confident in the intellectual argument for a better defended, better ordered Spain, and never seems to have shown serious doubt that his plans would succeed, or understood the growing hatred against his rule.

These plans take form first in Olivares' Unión de Armas, or 'Union of Arms' concept, put forward in 1624.

This would have involved the different elements of Philip's territories raising fixed quotas of soldiers in line with their size and population.

Despite being portrayed by Olivares as a purely military plan, it reflects Olivares' desire for a more closely unified Spain—although not, it is generally argued, a completely unified kingdom.

Olivares' 'Union of Arms' plan fails in the face of opposition from the provinces, in particular Catalonia, leading him to offer his resignation to the king in 1626; it is not accepted.

The subsequent years are to be challenging financially for Spain.

Philip has clear intentions to try and control the Spanish currency, which had become increasingly unstable during the reign of his father and grandfather, but in practice, inflation has soared.

Partly this is because in 1627 Olivares had attempted to deal with the problem of Philip's Genoese bankers —who had proved uncooperative in recent years—by declaring a state bankruptcy.

With the Genoese debt now removed, Olivares hopes to turn to indigenous bankers for renewed funds.

In practice, the plan is a disaster.

The Spanish treasure fleet of 1628 is captured by the Dutch, and Spain's ability to borrow and transfer money across Europe declines sharply.

The direct line of Mantua's Gonzaga family had come to an end in 1627 with the vicious and weak Vincenzo II, who on December 26 had died at the age of thirty-three on the same day that his niece Maria Gonzaga's marriage with Charles de Nevers was celebrated.

Nevers, the eldest son and heir of Charles, Duke of Nevers, Rethel and Mayenne, is the head of the cadet branch of the House of Gonzaga, and after Vincenzo II, heir of the Duchy of Mantua.

The Duke of Nevers is a son of Luigi, younger brother of Vincenzo II's grandfather.

Luigi had been naturalized French as Louis about 1550, and in 1566 had married the heiress of the duchies of Nevers and Rethel.

The French Crown would naturally prefer Nevers, a French peer, as ruler in Mantua.

Nevers arrives here in January of 1628 and proclaims himself its sovereign.

There are two rival claimants.

One is Charles Emmanuel I, Duke of Savoy, whose daughter Margerita is the widow of Francis IV.

Although their son had died an infant in 1612, it is their elder daughter Maria (1612-1660) who had married Charles de Nevers in 1627.

Charles Emmanuel bases his right to Mantua on his daughter's claim to a substantial portion of the Gonzaga realm, the Marquessate of Montferrat, which is demonstrably heritable by females since the Gonzagas had acquired it through marriage to Margherita Paleologa in 1540.

The other claimant is Ferrante II, Duke of Guastalla, a distant Gonzaga cousin who had voiced his claim but had not immediately placed troops in the field.

He is, however, supported by Emperor Ferdinand II, whose wife at the time, Eleanor of Mantua the elder (1598-1655), had been the sister of the last three Dukes of Mantua.

He seeks to reattach the Duchy of Mantua to the Holy Roman Empire; Ferrante, being in the Spanish-Imperial camp, is a useful tool to that purpose.

As the Thirty Years War wears on, it affects dynastic alliances.

Charles Emmanuel obtains support from the Habsburgs, who control Milan.

The resulting French-Habsburg war over the succession is just one of the many theaters of the Thirty Years War, fought all over Europe.

The initial attempt of Don Gonzalo Fernandez de Córdoba, Spanish governor of Milan, and Charles-Emmanuel is to partition the Mantuan-Montferrat patrimony, which lies to east and to west of Milan.

The Spanish minister supports the Guastalla claimant in Mantua, as the weaker of two neighbors, and the Savoy claimant in Montferrat, the lesser of the territories.

Friction between the confederates ensues, when Charles-Emmanuel moves his troops into more territory than had been agreed upon, laying siege to the town of Casale, capital of Montferrat.

The 1620s have been good years for Spanish foreign policy—the war with the Dutch had gone well, albeit at great expense, culminating in the retaking of the key city of Breda in 1624.

By the end of the decade, however, Philip's government is faced with the question of whether to prioritize the war in Flanders or Spain's relationship with France during the War of the Mantuan Succession.

Philip's advisors recommend prioritizing the war in Flanders, taking action to safeguard the Spanish Road to the Netherlands but at the cost of antagonizing Louis XIII.

Strategically this will prove disastrous.

Louis XIII of France and Cardinal Richelieu are concerned at home with Huguenot uprisings in Languedoc after the fall of La Rochelle in 1628, but the French nevertheless send forces to relieve Casale near the border with Milanese territory, besieged by a Habsburg army from Milan.

The French forces in March 1629 cross the Alps and on March 6 force Susa in Piedmont , ...

...deliver Casale from its besiegers on March 18 and ...

... take the fortress of Pinerolo on March 3.